Genome size and radiosensitivity: The size of the genome among different cell types and different species has been established by measurements of nuclear volume from many species, of DNA/cell from fewer, and for a very few species, size of the chromosome complement (DNA plus chromosomal proteins). Rate of mutation induction by radiation correlates well with radiosensitivity. But for cell killing by radiation, where the chromosomes are felt to be the pertinent target, neither nuclear volume nor DNA/cell yields a correlation with radiosensitivity that is consistent over the range of species tested. This work will obtain more estimates of size of the chromosome complement, for enough species to permit testing the correlation of this third genomic size parameter against radiosensitivity. Ratio of chromosomal to DNA amounts on isolated, purified chromatin from a few representative species will be measured. Capillary damage by fractionated radiation: Microangiographic techniques will be used to test if fractionated radiation regimes, as in cancer radiotherapy, cause the same damage to the capillary bed and circulation as has been shown to occur in mice following acute radiation, and doses will be compared for equivalent amounts of effect.